Simultaneous Determination of Tramadol and its Metabolite in Human Plasma by GC/MS

A simple and sensitive GC/MS method for the determination of tramadol and its metabolite (O-desmethyltramadol) in human plasma was developed and validated. Medazepam was used as an internal standard. The calibration curves were linear (r= 0.999) over tramadol and O-desmethyltramadol concentrations ranging from 10 to 200 ng/mL and 7.5 to 300 ng/mL, respectively. The method had an accuracy of >95% and intra- and interday precision (RSD%) of <= 4.83% and <= 4.68% for tramadol and O-desmethyltramadol, respectively. The extraction recoveries were 97.6 +/- 1.21% and 96.3 +/- 1.66% for tramadol and O-desmethyltramadol, respectively. The LOQ using 0.5 mL human plasma was 10 ng/mL for tramadol and 7.5 ng/mL for O-desmethyltramadol. Stability studies showed that tramadol and O-desmethyltramadol were stable in human plasma after 8 h incubation at room temperature or after 1 week storage at -20 degrees C with three freeze-thaw cycles. Also, this method was successfully applied to six patients who had been given an intravenous formulation of 100 mg tramadol with C-max results of 2018.1 +/- 687.8 and 96.1 +/- 22.7 ng/mL for tramadol and O-desmethyltramadol, respectively.